The invention concerns an electro-slag remelting furnace for consumable electrodes and comprising a mold for receiving a melt formed from the electrode material; at least one drive motor and at least one spindle and an associated spindle nut for vertical movement of the electrode; at least one guide column, which is provided for vertically guiding the consumable electrodes and which extends parallel with the spindle and relative to which the spindle is rotatably mounted at its two ends; and at least one clamping device for the consumable electrodes.
Such an electro-slag remelting furnace can be equipped with a mold of fixed location, known as a static mold, or with a mold that can be moved upwards and downwards and known as a sliding mold. With this equipment, either an electrode of suitable length can be fused to form a thicker block, or by means of two separate electrode-feed devices, one after the other, or to some extent simultaneously, to provide a block. The expression "change-over technique" has been introduced to designate the last-mentioned remelting process. Of particular importance in this process are the electrode-feed devices, since the remelting process is mainly determined and influenced by the rate of feed. It is necessary to be able to control the electrode feed with great accuracy and, particularly by the more extensive use of process computers, to be able to determine all the melting parameters, including the electrode feed rate, so that these parameters can be made available in advance in the form of a program for controlling the melting process.
U.S. Pat. No. 3,684,001 discloses a feed installation for electro-slag melting furnaces and wherein the electrode is moved downwards and upwards by means of hydraulic cylinders of fixed location. Such a form of construction offers, on the one hand, the advantage that the component of the feed installation that is located at the highest point is lowered as consumption of the electrode proceeds since when a plurality of hydraulic cylinders are arranged laterally of the electrode, the upwardly projecting thrust rods which are interconnected by a yoke from which the electrode is suspended, move downwards during the feed. This is of particular importance since, in the case of very long electrodes, very long feed paths must be present so that when melting begins, the height of the equipment is very great since at this moment the feed equipment is in its highest position. This necessitates particularly high workshop bays, since the crane installations required for charging the furnace must be provided at a high level if adequate unoccupied space above the furnace does not result from the following lowering movement of the feed installation. On the other hand, feed installations comprising hydraulic or compressed-air cylinders suffer from the disadvantage that unrequired lowering of the electrode takes place if the pipework develops leaks or becomes broken. Furthermore, in the case of such pressure-medium drives, the control of the very slow feed rate during melting off is possible only at considerable expense if a completely continuous and uniform electrode feed is to be obtained.
Electro-mechanical drives in conjunction with screw-threaded spindles, particularly ball-mounted spindles, are especially advantageous for providing a high-precision electrode feed. Because of the low friction involved in spindle drives of this kind, no appreciable locking effect ("slip-stick effect") occurs, and by the use of a multi-motor drive it is possible to achieve very high accuracy in the regulation of the feed in greatly varying speed ranges. The known electro-mechanical drives comprising screw-threaded spindles suffer from other disadvantages, however.
U.S. Pat. Nos. 2,857,445 and 3,057,935 disclose remelting furnaces which, with the exception of the use of slag, correspond to the initially described type of furnace. In both cases the screw-threaded spindles of fixed location are arranged laterally of the electrode and are mounted at their ends in a portal-like frame. This frame determines the height of the entire furnace, which height cannot be altered. The spindle nuts are mounted in a transverse member which is movable in the vertical direction on two vertical guide columns, likewise of fixed location. The use of more than one spindle and spindle nut renders the furnace construction expensive; furthermore, the furnace is difficult of access from above.
U.S. Pat. Nos. 3,379,238 and 3,393,264 disclose similar furnace constructions wherein the guide columns are of fixed location and form a portal-like frame. In these two cases, a central screw-threaded spindle of fixed location is provided, which is located within a tube which also forms the electrode-retaining bar, which is movable on the guide columns by means of sliding guides. The thus imposed unalterable height of the construction is substantially greater than in the case of the above-described furnaces, since because of the telescopic interengagement of the spindle and the electro-retaining bar, the height of the portal-like frame must be such that it is equal to at least twice the length of the spindle, i.e. twice the maximum length of the electrode. The length of the spindle in turn determines the maximum stroke of the electrode-clamping device. The screw-threaded spindle together with the drive units must therefore be located at so high a level that, for the maximum length of electrode, the electrode-retaining bar together with the spindle nut can be brought into the highest position. This maximum height then determines the height of the entire installation.
Furthermore, the known furnaces cannot be used for, and indeed are not designed for, the above-described "change-over technique". Particularly in the case of electro-slag remelting furnaces involving the use of change-over technique and wherein the electrodes are remelted one after the other to form a large block, heights of construction result for which the existing workshop bays and levels of crane track are inadequate, so that considerable expenditure is necessary for increasing the size of the bays or for providing pits for the foundations.
The known solution involving the telescopic engagement of the screw-threaded spindle in the electrode-retaining bar is accompanied by the further disadvantage that additional guides must be provided for the spindle nut and the electrode-retaining bar in order to take up the torque transmitted to the electrode-retaining bar and to prevent deflection of the electrode bar and therefore the electrode, as well as to avoid bending of the spindle.
U.S. Pat. No. 3,739,066 discloses an electro-slag remelting furnace comprising a plurality of guide columns which can be raised and lowered by means of screw-threaded spindles of fixed location. The "change-over technique" can also be carried out with this known installation, since the guide columns together with the electrode-clamping device secured to them can be lowered and swiveled independently of each other. In the case of this electro-slag remelting furnace, the free space above the mold is increased by lowering the guide columns. However, though having proved successful in large installations, this form of construction, when used in connection with smaller furnaces, suffers from the disadvantage that the length of the guide columns corresponds to the height of the furnace, so that an expensive furnace construction results. Furthermore, the spindles are of fixed location, whereas the spindle nuts secured to the guide columns are vertically displaceable. This results in compressive loading of the spindles which consequently must be of large cross-section. Because of their length, the guide columns must of necessity extend along the periphery of the mold, so that a gallows-like construction results which leads to large bending moments in the guide columns. In particular, however, because of the exposed current loops and the associated high inductive losses, the known construction does not permit the use of current-supply means operating on mains frequency, so that the known installation has to operate on alternating currents of extremely low frequency, for example 1 to 5 Hz, and this requires the use of expensive inverters.